The present invention relates to fuel compositions having reduced nitrogen oxide (NOx) emission, more particularly, to high stability, low emission, fuel emulsion compositions for use in internal combustion engines.
Nitrogen oxides comprise a major irritant in smog and are believed to contribute to tropospheric ozone, which is a known threat to health. Environmental considerations and government regulations have increased the need to reduce NOx production. Various methods for reducing NOx production include the use of catalytic converters, engine timing changes, exhaust recirculation, and the burning of “clean” fuels. These methods are generally too expensive and/or too complicated to be placed in widespread use.
High flame temperatures reached in internal combustion engines, for example diesel-fueled engines, increase the tendency for the production of nitrogen oxides (NOx). These are formed from both the combination of nitrogen and oxygen in the combustion chamber and from the oxidation of organic nitrogen species in the fuel. The rates at which NOx are formed is related to the flame temperature; a small reduction in flame temperature can result in a large reduction in the production of nitrogen oxides.
It has been shown that introducing water into the combustion zone can lower the flame temperature and thus lower NOx production, however; the direct injection of water requires costly and complicated changes in engine design. Further attempts to use water to reduce flame temperature include the use of aqueous fuels, i.e., incorporating both water and fuel into an emulsion. Problems that may occur from long-term use of aqueous fuels include engine corrosion, engine wear, or precipitate deposition, which may lead to engine problems and ultimately to inoperability. Problematic precipitate depositions include coalescing ionic species resulting in filter plugging and inorganic post combustion deposits resulting in turbo fouling. Another problem related to aqueous fuel compositions is that they often require substantial engine modifications, such as the addition of in-line homogenizers, thereby limiting their commercial utility.
Another method for introducing water into the combustion area is to use fuel emulsions in which water is emulsified into a fuel continuous phase, i.e., invert fuel emulsions. A problem with these invert fuel emulsions is obtaining and maintaining the stability of the emulsion under conventional use conditions and at a reasonable cost. Gravitational phase separation (during storage) and high temperature high pressure/shear flow rate phase separation (in a working engine) of these emulsions present the major hurdle preventing their commercial use.
The present invention addresses the problems associated with the use of invert fuel emulsion compositions by providing a stabile, inexpensive invert fuel emulsion composition with the beneficial reduction in NOx and particulate emissions.